1. Field of the Invention
The present invention relates to electrical terminators, and more specifically, to a terminator system for use in signal communication between a sending circuit and a receiving circuit.
2. Description of the Related Art
High speed data communication integrated circuit chips are known. A conventional high speed data communication integrated circuit chip includes a receiver and a driver. The driver of one conventional high speed data communication chip connects to a receiver of another high speed data communication chip through a chip communication signal line.
The driver of the sending data communication chip is connected to the chip communication signal line through a conventional electrical terminator. Similarly, the receiver on the receiving communication chip is also connected to the communication signal line through a conventional electrical terminator. An on-chip conventional electrical terminator consists of multiple transfer gates that gate an electrical signal from the driver onto the communication signal line or receive the electrical signal from the communication signal line and gate it to the receiver.
The conventional electrical terminator includes a fixed resistance value that tries to match the signal line characteristic impedance. If the resistance value changes, however, the resistance value of the conventional terminator is unable to match the signal line characteristic impedance of the communication signal line. This significantly reduces the reliability of communication signals sent between the driver and the receiver. For example, there may be up to fifty percent degradation in a communication signal sent between the driver and the receiver when the resistance value of a terminator does not match the line characteristic impedance of the communication signal line.
A problem with conventional terminators is that they are not consistently reliable for transmitting data because the resistance value of the terminator can change due to a variety of conditions. For example, the resistance of the transfer gates is highly dependent upon the different manufacturing processes used to create them. This results in different resistance values for each manufactured conventional terminator. Different resistance values for each different manufacturer degrades data passing through the conventional terminator because the line characteristic impedance of the signal line to connect two conventional terminators may only match one conventional terminator and not the other or may not match either conventional terminator.
Another problem with conventional terminators is that the resistance value may vary depending on the supply voltage used with the transfer gates. When the supply voltage changes, the resistance value of the conventional terminator also changes. Therefore, for communication chips that may be connected to a variety of supply voltage sources, there may be a degradation of data transferred through the conventional terminators due to resistance value fluctuations.
Another problem with conventional terminators is that they are highly sensitive to on-chip temperature. As the on-chip temperature changes, the resistance value of the conventional terminator also changes. For example, as the clock speed for high speed communication integrated circuit chips increases, the chip temperature also increases. This causes the terminator resistance value to change so that there is a degradation of data passing through the conventional terminator.
In every instance where there is a change in the resistance value of the conventional terminator, the result is a degradation of performance of the integrated circuit chip. For example, there may be a decrease in communication signal quality, a decrease in communication signal accuracy leading to a decrease in communication speed, and/or a decrease in overall chip speed because communication signals must be re-transmitted.
Therefore, there is a need for an electrical system having an electrical termination system that provides (1) consistent resistance characteristics and that (2) may be used in a variety of electrical circuits and systems where there must be a match between the impedance characteristics of an electrical signal line and the sending and/or receiving circuits and systems.
A system and a method in accordance with the present invention satisfies a need for matching a resistance value of a termination element to a line characteristic impedance of an electrical signal line. A system and a method in accordance with the present invention also satisfies a need for generating an adjustment signal for adjusting a resistance of a termination system.
The present invention includes a termination system in an electrical system in accordance with the present invention. The electrical system may be an integrated circuit microchip or chip. The chip may be, for example, a high speed data communication integrated circuit chip or a router integrated circuit chip that drives or receives electrical signals to or from another chip or chips, for example, other router integrated circuit chips.
A termination system in accordance with the present invention includes a termination element, a reference resistance system, and a feedback control system. The termination element includes one or more transfer gates. Each transfer gate may be comprised of one or more transistor elements, for example, MOSFET transistor elements or BJT transistor elements. The termination element is connected to a driver system and an electrical signal line. The reference resistance system provides a resistance value that is substantially equivalent to a line characteristic impedance of the electrical signal line. The feedback control system is connected to the reference resistance system and the termination element.
A resistance value of the termination element is matched to the line characteristic impedance of the electrical signal line so that the electrical signal can be sent from the driver system through the electrical signal line without electrical reflection. Reducing or eliminating electrical reflection maintains the accuracy and quality of the electrical signal. To match the resistance of the termination element to the impedance of the electrical signal line, the feedback control system generates an adjustment signal that accordingly adjusts the resistance of the termination element. It is noted that the electrical signal line may be any conduction line, for example, a wire, a cable, a PCB trace, a chip etching, or the like.
To generate the adjustment signal, the feedback control system uses the reference resistance system that has a resistance that is substantially equivalent to the line characteristic impedance of the electrical signal line. The feedback control system can continuously compare an on-chip resistance to the resistance of the reference resistor system. Using this comparison, the feedback control system can increment or decrement the adjustment signal accordingly to switch on or switch off transfer gates in the termination element. By switching transistors of the transfer gates on or off, the resistance of the termination element can be matched to the line characteristic impedance of the electrical signal line.
A feedback control system in accordance with the present invention includes a comparison system, a counter system, and a termination control code filter. The comparison system includes an on-chip resistance system that is connected to the reference resistance system. The comparison system is connected to the counter system. The counter system is connected to the termination control code filter and the on-chip resistance system in the comparison system. The terminator control filter is connected to the termination element.
The on-chip resistance system includes one or more transistor elements that provide a variable resistance depending on whether they are in an on state or an off state. The comparison system compares the resistance value of the variable on-chip resistance system to the resistance value of the reference resistance system. Based on this comparison, the comparison system generates a comparison signal that is sent to the counter system. If the resistance of the on-chip resistance system is less than the resistance of the reference resistance system, the comparison signal is a down signal. If the resistance of the on-chip resistance system is greater than the resistance of the reference resistance system, the comparison signal is an up signal.
The counter system receives the comparison signal and generates a control code. The control code is an increasing counter signal if the up signal is received and is a decreasing counter signal if a down signal is received. The termination code control filter receives the control code and generates the adjustment signal for the termination element. Specifically, if the control code is an increasing counter signal, the transistors in the termination element are turned on so that their resistance is decreased to match the line characteristic impedance of the electrical signal line. If the control code is a decreasing counter signal, the transistors in the termination element are turned off so that their resistance is increased to match the line characteristic impedance of the electrical signal line.
The present invention allows for signal transmission having increased quality and accuracy because the on-chip resistance value of the termination elements can be advantageously matched to the line characteristic impedance of the electrical signal lines coupled to the terminators. Moreover, the present invention increases overall system speed and efficiency because there is no signal reflection, and therefore signal quality is high and accurate.
The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter.